Aqueous polymer dispersions and aqueous coating materials based on aqueous polymer dispersions are known. EP-A-469,646, for example, describes aqueous polymer dispersions of hybrid polymers, which are used for the production of aqueous coating materials. The hybrid polymers are prepared by polymerizing ethylenically unsaturated monomers in the presence of an epoxide-containing reaction product of n mol of a bisepoxide compound and n-1 mol of a dicarboxylic acid, which product has itself been reacted with unsaturated fatty acids. Following neutralization of the acid groups contained in the polymer, the hybrid polymer is dispersible in water. From the aqueous polymer dispersions prepared in this way it is possible to product aqueous coating materials which, disadvantageously, give coating films which have a tendency to yellow, especially when relatively long baking times and/or relatively high baking temperatures are employed.
The object of the present invention is to provide aqueous polymer dispersions from which it is possible to produce aqueous coating materials which can be used to produce coating films in which the above-described disadvantages are reduced or absent and which additionally have good surface properties, in particular a high acid resistance and scratch resistance.
This object is surprisingly achieved by the provision of aqueous polymer dispersions which can be prepared in that
(A) 1.0 part by weight of a mixture of PA1 (B1) from 0.5 to 9.0 parts by weight of a reaction product of PA1 (B2) from 0.5 to 9.0 parts by weight of a reaction product of component (b1) and PA1 (B3) from 0.5 to 9.0 parts by weight of a reaction product of component (b1) and
(a1) from 2.5 to 13% by weight of an ethylenically unsaturated monomer which contains acid groups, or of a mixture of such monomers, and PA2 (a2) from 87 to 97.5% by weight of an ethylenically unsaturated monomer which is free from acid groups, or of a mixture of such monomers, PA2 (b1) a compound which contains on average per molecule at least 1.5 epoxide groups, or a mixture of such compounds, and PA2 (b2) a mixture of PA2 (b3) a monoester of an ethylenically unsaturated dicarboxylic acid and a saturated fatty alcohol, or a mixture of such monoesters, PA2 (b4) a mixture of components (b21), (b22) and (b3) or a mixture of components (b21) and (b3) or a mixture of components (b22) and (b3).
the sum of the percentages by weight of components (a1) and (a2) always being 100% by weight, are subjected to free-radical polymerization in the presence of
(b21) an ethylenically unsaturated monocarboxylic acid having 3-8 carbon atoms, or a mixture of such monocarboxylic acids, and PA3 (b22) a saturated fatty acid, or a mixture of saturated fatty acids,
or in the presence of
or in the presence of
and the resulting polymerization product is converted, during or after the neutralization of at least 20 percent of the acid groups contained in the polymerization product, into an aqueous polymer dispersion, components (b1), (b2), (b3) and (b4) being reacted with one another in proportions such that components (B1), (B2) and (B3) contain on average per molecule not more than 0.25 epoxide groups and at least 0.4 ethylenically unsaturated groups which derive from component (b21) and/or component (b3) .